It is necessary to maintain the integrity of structural objects and components that have been subjected to wear and stress from the hazards of the environment in which such objects and components operate. Accordingly, it is desirable to test such structural objects and components periodically to determine whether they have degraded strength or reliability due to such flaws as surface cracks, corrosion, disbonds, and the like. While in some instances it is possible to remove the object to be tested from its location of use and perform a test of its integrity while it is mounted on a test stand in a laboratory using laboratory instruments, this is not always possible or practicable. In many instances, the test object is very large and/or is integrated into a larger structure in a manner that makes its removal difficult if not impossible to remove for remote testing in a laboratory.
Further, it is desirable to perform nondestructive evaluation (NDE) tests on objects. An advantage of NDE tests is that they do not permanently alter an object in an undesirable manner, which may render the test object useless for its intended purpose. Consequently, there is a need to develop methods and systems for NDE tests on objects without having to remove the objects from their location and environment of use.
Nondestructive evaluation systems and methods have been developed to provide non-contact inspection of components and structures in the field to detect flaws and otherwise determine the integrity of such structures and components. One form of NDE is thermographic inspection, in which a thermal pattern at the test object's surface is created and differences in the surface temperature are interpreted to determine the existence of flaws. One type of active thermographic inspection is infrared thermography. A form of infrared thermography is vibrothermography, which uses amplitude modulated or pulses of ultrasonic waves to excite internal features of the test object. A source or mechanical vibration transmits ultrasonic vibrations in the test object, which cause the surfaces defining the flaw or defect to vibrate at different frequencies relative to each other creating heat. The heat generated at the location of the flaw raises the temperature of the test object at the flaw above that of the remainder of the test object. This area of greater temperature is apparent on a thermal image of the test object taken by an infrared camera. The locations of the defects are thus detected by infrared cameras through the process of mapping temperature distribution on the surface of the object.
A disadvantage with such systems is that they are static. That is, they require structure that places them in close proximity with the object to be tested, and that object must not be moving to enable the system and method to be performed on a specific test area. Such systems may be appropriate for non-moving objects, such as parked vehicles and aircraft. However, there is a need for a method and system for nondestructive evaluation of moving vehicles, such as railroad cars, and for traversing extremely large objects, such as railroad rails.